A valve disclosed in Patent Literature 1, for example, includes a seal member made of elastic material and having a donut shape. The seal member is provided to prevent a fluid in a conduit from leaking out through a clearance between a valve shaft and bearing. The bore of an inner diameter portion of the seal member is supported by the valve shaft. The seal member is arranged between the bearing and a plug that is disposed axially opposite the bearing.
When the fluid flows in the conduit to cause a difference in pressure between the inside and outside of the conduit, the seal member receives pressure from the side of the conduit. This pressure causes the seal member to move in an axial direction toward the plug and change its shape. As a result, the outer diameter portion of the seal member is pushed against the plug. Thereby, the inner diameter portion of the seal member and an outer circumferential surface of the valve shaft are in close contact with each other and are sealed together, and the outer diameter portion of the seal member and the plug are in close contact with each other and are sealed together. Consequently, it is possible to prevent the fluid from leaking out beyond the plug.
Patent Literature 2 discloses a valve having a bearing bushing for supporting a valve shaft. The bearing bushing has a sealing function to prevent an exhaust gas from leaking out through the periphery of the valve shaft. The bearing bushing is made of carbon material and has a cylindrical shape. An end surface of the bearing bushing is in contact with an end surface of the valve and is pushed by the end surface of the valve. Thereby, the leakage of the fluid is prevented.
Note that the valve disclosed in Patent Literature 2 is intended to be used in a high-temperature atmosphere. So, the valve and the valve shaft are made of titan material. Valves made of titan material provide good rotational slidability between the valve and the bearing bushing made of carbon material even in a high-temperature atmosphere.